Psoriasis is a chronic inflammatory skin disease that manifests as erythematous, dry, scaling plaques resulting from hyperkeratosis. The plaques are most often found on the elbows, knees and scalp, though more extensive lesions may appear on other parts of the body, notably the lumbosacral region. The most common treatment of mild to moderate psoriasis involves topical application of a composition containing a corticosteroid as the active ingredient. While efficacious, corticosteroids have the disadvantage of a number of adverse effects such as skin atrophy, striae, acneiform eruptions, perioral dermatitis, overgrowth of skin fungus and bacteria, hypopigmentation of pigmented skin and rosacea.
For many years, however, an advantageous non-steroidal treatment of psoriasis has consisted in topical treatment with the vitamin D analogue compound, calcipotriol, formulated in an ointment composition (marketed as Daivonex® or Dovonex® ointment by LEO Pharma) in which the calcipotriol is present in solution or a cream composition (marketed as Daivonex® or Dovonex® cream by LEO Pharma). The solvent in the ointment composition is propylene glycol which has the advantage of enhancing penetration of the active ingredient into the skin, leading to an improved efficacy, but which is also known to act as a skin irritant. Thus, it has been reported that the inclusion of propylene glycol in topical compositions frequently causes patients to develop contact dermatitis (one study reported a number of irritant reactions to propylene glycol of 12.5%, cf. M. Hannuksela et al., Contact Dermatitis 1, 1975, pp. 112-116), and the number of irritant reactions increases when propylene glycol is used in high concentrations (as reviewed by J. Catanzaro and J. Graham Smith, J. Am. Acad. Dermatol. 24, 1991, pp. 90-95). Due to the improved penetration of calcipotriol into the skin resulting, inter alia, from the presence of propylene glycol, Daivonex® ointment has been found to be more efficacious in the treatment of psoriatic lesions than Daivonex® cream, but has also caused skin irritation in a significant proportion of psoriasis patients.
It is therefore an object of the invention to provide a topical composition comprising a vitamin D derivative or analogue as the active ingredient, which has skin penetration and biological activity properties comparable to those of Daivonex® ointment, but which does not contain propylene glycol as the solvent.